System and method for generating effective layout constraints for a circuit design or the like

• US 6,058,252 A
• Filed: 08/13/1997
• Issued: 05/02/2000
• Est. Priority Date: 01/19/1995
• Status: Expired due to Term

• Current Assignee: Synopsys Incorporated
• Original Assignee: Synopsys Incorporated
• Inventors: Walker, Robert L., Scott, Kenneth E., Noll, Mark D.
• Primary Examiner(s): Teska, Kevin J.
• Assistant Examiner(s): Fiul, Dan
• Application Number:
  US08/910,803
• Time in Patent Office: 993 Days
• Field of Search: 364/488, 364/489, 364/490, 364/491, 364/578, 395/500
• US Class Current: 716/113
• CPC Class Codes: G06F 30/3312 Timing analysis
• CPC Class Codes: G06F 30/3315 using static timing analysis [STA]
• CPC Class Codes: G06F 30/39 Circuit design at the physical level physical level design for reconfigurable circuits G06F30/347

Abstract

A computer system and computer implemented method for deriving constraints with which to direct automatic integrated circuit layout is disclosed. The present invention is particularly adapted for use in the design of large integrated circuits with complex synchronous timing behavior. Preferably, the invented computer system includes means for storing a netlist data structure within a storage means is provided, the netlist data structure representing a circuit configuration having a plurality of circuit elements and representing static timing information for the circuit configuration; means for selecting specified circuit elements to be used for generating the layout constraints, whereby the specified circuit elements that are selected are fewer than, i.e. represent a proper subset of, the plurality of circuit elements of the circuit configuration; means for identifying a most critical path through each of the specified circuit elements based upon the static timing information, whereby preferably the most critical path is that path having the least slack defined as the difference between a required time at which a signal should reach the specified circuit element and an arrival time at which the signal is expected to reach the specified circuit element; and means for generating layout constraints from the most critical path through each of the specified circuit elements, whereby at least one constraint is generated covering each of the specified circuit elements. Also disclosed is a feature whereby any paths that do no meet specified filter criteria, and paths that are duplicates of others, are discarded, thereby retaining only irredudant critical paths on which to base layout constraints.

Claims

1. A digital computer system for processing a netlist to generate circuit layout constraints for use by an identified target circuit placement and signal routing tool, the system including a computer having storage means and execution means, the system comprising:

means for storing a netlist data structure in said storage means, said netlist data structure representing a circuit configuration having a plurality of circuit elements and said netlist data structure representing static timing information for said circuit configuration;

means for selecting specified circuit elements to be used for generating said layout constraints, said means for selecting operating in such manner as to select fewer than all of the plurality of circuit elements of the circuit configuration;

means for identifying a most critical path through each of said specified circuit elements based upon said static timing information represented in said netlist data structure; and

means for generating circuit layout constraints from the most critical path through each of said specified circuit elements, wherein said generated layout constraints include at least one constraint involving circuit placement or signal routing, wherein said generating means including means for extracting and formatting irredundant layout constraints for use by an identified target circuit placement and signal routine tool,

whereby at least one such circuit layout constraint is generated covering each of said specified circuit elements.

2. The system of claim 1, wherein said circuit elements include ports and nets.

3. The system of claim 2, wherein said specified circuit elements are nets.

4. The system of claim 2, wherein said specified circuit elements are driver pins.

5. The system of claim 2, wherein said specified circuit elements are load pins.

6. The system of claim 1, wherein said most critical path through each of said circuit elements is a path having the least slack for said circuit element, wherein slack is the difference between a required time at which a signal should reach the specified circuit element and an arrival time at which the signal is expected to reach the specified circuit element.

7. The system of claim 2, wherein said circuit elements further include net segments.

8. The system of claim 7, wherein said circuit elements further include driver pins and load pins.

9. The system of claim 8, wherein said circuit elements further include cell instances.

10. A digital computer system for processing a netlist to generate circuit layout constraints for use by an operatively connected circuit placement or signal routing program, the system including a computer having a memory for data storage and a processor for program execution, the computer system comprising:

a memory structure for storing a netlist data structure that represents a circuit configuration having a plurality of circuit elements, said structure further representing static timing information for said circuit configuration;

a selector for selecting specified circuit elements to be used for generating such layout constraints whereby only a proper subset of the plurality of circuit elements of said circuit configuration are selected as such specified circuit elements;

a timing analysis module for identifying a most critical path through each of said specified circuit elements based upon said static timing information represented in said netlist data structure;

a circuit layout constraint module for generating layout constraints from the most critical path through each of said specified circuit elements, wherein said generated layout constraints include at least one constraint involving circuit placement or signal routing, whereby at least one such circuit layout constraint is generated covering each of said specified circuit elements; and

a target circuit placement and signal routing tool responsive to said circuit layout constraint module and to said memory structure storing said netlist data structure for performing circuit placement and signal routing to implement said circuit configuration within said generated layout constraints.

11. The system of claim 10, wherein said circuit elements include ports and nets.

12. The system of claim 11, wherein said specified circuit elements are nets.

13. The system of claim 11, wherein said circuit elements further include net segments.

14. The system of claim 13, wherein said circuit elements further include driver pins and load pins.

15. The system of claim 14, wherein said circuit elements further include cell instances.

16. A digital computer system for processing a netlist to generate circuit layout constraints, the system including a computer having a memory for data storage and a processor for program execution, the computer system comprising:

a memory-based technology library of circuit blocks, said library containing static timing information characteristic of each circuit block;

a memory structure for storing a netlist data structure that represents a circuit configuration having a plurality of circuit elements, said structure further representing static timing information for said circuit configuration with said static timing information being supplied by said technology library consistent with said characteristic;

a selector for selecting specified circuit elements to be used for generating such layout constraints;

a timing analysis module for identifying an irredundant critical path through each of said specified circuit elements based upon said static timing information represented in said netlist data structure;

a circuit layout constraint module for generating circuit layout constraints from the irredundant critical path through each of said specified circuit elements, said generated circuit layout constraints including circuit placement and signal routing constraints; and

a mode control input to said circuit layout constraint module for indication by a user of a desired format for the inputs or outputs to or from said circuit layout constraint module,

whereby at least one circuit layout constraint is generated covering each of said specified circuit elements.